In the United States, approximately 10 to 11 million tons of old asphalt shingle roofing (“tear-offs”) is removed from existing building each year, and about 1.0 million tons of factory rejects and tab cut-outs (“factory scrap”) are generated each year. The exact composition of a particular roofing shingle depends on the manufacturer and the roofing application, but the shingle manufacturing process is similar in each instance.
The shingle manufacturing process begins with a layer of organic (cellulose or wood fiber) or fiberglass backing felt. The felt is impregnated with liquid asphalt, then coated on both sides with additional asphalt. The asphalt used as the saturant is of a different type than the asphalt used as the coating, but both are harder than asphalt generally used in pavement. Both types of asphalt are “air-blown”, or bubbled, during production, a process that incorporates oxygen into the asphalt and further increases the viscosity. Powdered limestone (70% passing the No. 200 sieve) is also added to both types of asphalt as a stabilizer.
Once coated with the appropriate thickness of asphalt, one side of the shingle is then surfaced with granules for protection against physical damage, and damage from ultraviolet rays of the sun. The granules which are exposed in the roofing application are comprised crushed rock coated with ceramic metal oxides, and the headlap granules are coal slag. Both types of aggregate are relatively uniform is size, most ranging from 0.3-2.36 mm, and both are hard and angular.
Finally, a light coating of fine sand (<0.425 mm) is applied to the back surface to prevent the individual shingles from adhering to each other during packaging and transport.
There has been a significant interest in and development of several systems and methods for recycling both new and used asphalt roofing shingles, and for using the recycled material in hot and cold paving compositions. To date, however, none of these prior art system and methods have resulted in an economically and technically viable solution.
For example, currently one methodology and system utilizes a 400 hp grinder is used to chip shingles into ⅜ inch pieces at ambient temperatures so that the pieces can be used in asphalt for roads. However, this process consumes a tremendous amount of energy and is environmentally unfriendly (emitting large quantities of dust). The material produced is unsuitable to most paving companies because all of the nails are not removed, the size of the material is so large that little of the “asphalt” value in the roofing shingles is released to be used for asphalt in the paving composition, and the shingles are inconsistent containing unknown amounts of fiberglass and organic shingles mixed together.
Another problem with the current chipped shingles used in paving compositions is that paving companies do not want plastic film previously on the back of the shingles to show up in the finished road.
In the paving market, the “fines” from recycled asphalt such as asphalt shingles are a huge problem. Fines are defined as particles that are 200 mesh or smaller. The fines wash the aggregate before it is introduced into the road mix. If there is too high of a level of fines, it causes over-compaction of the road surface. It is preferred that a certain amount of air “voids” are in the mix. Fines are undesirable because they decrease voids and the voids are necessary for compaction and road longevity. The fines also create problems with the roller procedure and cause over compaction, which may cause premature failure of the road.
Road asphalt producers are typically concerned with “rock dust.” If crushed rock from the roofing shingles is used as filler in asphalt based road material, it can cause cracking and ultimately product failure. The paving industry experienced wide spread failure due to this problem. This has also been a barrier to recycling technologies that crush the granules.
Accordingly, what is needed is and asphalt shingle recycling system and method which addresses the problems currently found in the prior art systems. The system should have a lower energy usage, such as 140 hp motor rather than the high energy usage of 400-500 hp currently seen in systems. The system should be environmentally friendly, reducing or eliminating the clouds of dust that are emitted into the atmosphere from prior art systems and additionally should remove all nails and also remove the reinforcing component of the shingle (fiberglass or cellulose) in order to achieve consistency in the milling process. The present invention addresses all of the issues currently found in prior art systems.